1. Field of the Invention
The present invention relates to a catheter tube used for a blood vessel catheter, for instance and a method of manufacturing the catheter tube.
2. Description of the Prior Art
Generally, in performing selective angiography or vasodilation, various catheters such as an angiography catheter, a guiding catheter or a balloon catheter or the like are used. In these catheters, it is usually required to have such an excellent manipulatability that can be selectively inserted into a blood vessel system of complicated pattern quickly and securely.
In more detail, the above-mentioned manipulatability of the catheter includes pushing characteristics, torque transmission characteristics, follow-up characteristics and kink-resistant characteristics. The pushing characteristics means that when the catheter is pushed into a blood vessel by an operator, a pushing force of the operator can be securely transmitted from the base end side to the tip side of the catheter. The torque transmission characteristics mean that a rotative force applied to the base end side of the catheter can be securely transmitted to the tip side thereof. The follow-up characteristics mean that when the catheter is inserted into a curved blood vessel, the catheter can travel smoothly along a guide wire going ahead without injuring the inner wall of the blood vessel (hereinafter, referred to as "follow-up to the guide wire" or simply "follow-up"). The kink-resistant characteristics mean that when the catheter is extracted after having reached at a destination, the catheter will not be bent at a curved or bent position of the blood vessel.
In order to improve the pushing and transmission characteristics, it is so far known that the catheter tube excepting the tip portion thereof is preferably formed of a relatively hard material. Further, in order to improve the follow-up characteristics, it is so far known that the tip portion thereof is preferably formed of a relatively soft material.
On the basis of this knowledge, Japanese Laid-open Patent Publication No. 59-156353 discloses a catheter tube in which a tubular base portion formed of nylon is fused integrally into a tip portion formed of polyether-polyamide copolymer so as to provide an appropriate flexible tip portion of the catheter tube. In this catheter tube, however, since two different materials must be fused for connection, there is a problem in that the connected portion is easily broken off. Further, there is another problem in that a stepped portion is likely to be formed on the outer surface of the catheter tube, which results in that the inner wall of the blood vessel is likely to be injured when the catheter tube is being inserted thereinto. Furthermore, since the rigidity of the catheter tube changes abruptly at the connected portion, the connected portion is likely to be bent, so that the kink-resistant characteristics are deteriorated. In addition, there is a further problem in that a special manufacturing installation is required for fusing the polymers and a complicated manufacturing process is inevitably required.
Further, Japanese Utility Model Publication No. 62-17082 discloses a catheter tube which comprises an outer tube and an inner tube inserted into the outer tube excepting the tip portion of the outer tube, in which the outer tube is formed of a silicone rubber and the inner tube is formed of a hard resin selected from the group consisting of polyethylene, polypropylene, fluororesin and hard vinyl chloride resin. In the catheter tube as disclosed above, however, since a stepped portion which corresponds to the thickness of the inner tube is unavoidably formed within the inner hollow portion of the tube at the boundary part between the double-tubes portion (the main body portion 4) and the single-tube portion (the tip portion 3), the tube is likely to be broken off at this stepped portion, thus deteriorating the kink-resistant characteristics.
Moreover, U.S. Pat. No. 4,636,346 discloses a guiding catheter having a catheter tube which comprises a main portion having three-layers structure and a tip end portion having two-layers structure and extending toward the tip of the catheter from the main portion. The main portion is composed of an inner tube, an intermediate layer and an outer tube. The tip end portion is composed of an inner tube and an outer tube, but no intermediate layer is provided. However, the main portion of the catheter tube, having the three-layered structure, has bending rigidity that is constant in the longitudinal section thereof and the bending rigidity changes abruptly at the boundary part between the main portion and the tip portion having the two-layered structure because of the presence or absence of the intermediate layer. As a result, the tube is likely to be broken off at this boundary part, thus deteriorating the kink-resistant characteristics.